Log Scale Calculator

Calculate board feet in a log

Measure the small end, inside the bark. That's the number every one of these rules actually uses — see why below.

How it's calculated

All three scales measure the log's small-end diameter inside bark and its length, then apply a different assumption about saw kerf and taper. Here's each formula, plain.

Doyle Rule

Board feet = (D − 4)² × L ÷ 16, where D = small-end diameter in inches, L = length in feet.

Devised by New York lumberman Edward Doyle around 1825, built around the heavy saw kerf and slabbing losses of early sawmills. Subtracting a flat 4 inches before squaring the diameter punishes small logs hard — a log under about 5 inches scales at close to zero — and past roughly 28 inches it starts overestimating instead. Despite that, Doyle remains the traditional rule across the eastern and southern United States, and it's still what many hardwood mills print on a scale ticket.

Scribner Decimal C

Scribner has no clean formula. J.M. Scribner built the original rule in the 1840s by drawing actual saw-kerf diagrams of boards packed into a circle for each diameter, then reading the board footage off the diagram — not by computing it. "Decimal C" rounds those diagram values to the nearest 10 board feet and drops the last digit for a shorter scale-stick reading, then multiplies back by 10 for the real total. Because it comes from a diagram rather than an equation, every calculator that claims a smooth "Scribner formula" is really an approximation — often a rough one. This calculator uses the actual published Scribner Decimal C table for the standard 6–30 inch, 6–16 foot range, the same table foresters, scalers, and log buyers have used for over a century, rather than approximate it.

International ¼″ Rule

Originally derived by Judson F. Clark in 1906 and refit by L.R. Grosenbaugh in 1948, this is the only one of the three actually built to model a real saw kerf (a genuine ¼ inch) and the log's real taper, rather than treating the whole log as one plain cylinder. It's computed in 4-foot sections along the log, allowing ½ inch of taper per section: each section's board-foot volume is ⅓⅔ × (0.22d² − 0.71d) — more precisely 19⁄21 × (0.22d² − 0.71d) — where d is that section's own small-end diameter, and a final partial section is pro-rated by its share of a full 4 feet. It's generally considered the most accurate of the three published rules, and it's the rule LogScanner and LogMaster compute internally. Numbers here can differ from a printed International table by a board foot or two — this calculator runs the rule directly instead of reading a table, and century-old tables carry their own small rounding.

Common sizes at 12‑foot length

Works without JavaScript, and a fast sanity check either way — small-end diameter down the side, all three scales in board feet.

Which scale should I use?

Doyle is the traditional rule across the eastern and southern United States — a lot of Appalachian and Southern hardwood mills still write Doyle on the scale ticket. Scribner is the standard out West, especially on U.S. Forest Service and other public timber sales through the Pacific Northwest and Inland Northwest. International ¼″ is the newer, more accurate rule — the only one of the three actually derived to model real kerf and taper instead of a bare cylinder — and it's what shows up in forest-mensuration textbooks, government cruising work, and the LogScanner and LogMaster apps. None of the three is universally "correct." Which one matters mostly comes down to who's buying the logs and what region you're in — if nobody's telling you which to use, International ¼″ is the one to trust.

Why small-end diameter?

Every one of these rules measures the small end of the log, inside the bark — never the middle, never the butt. That's not arbitrary: the small end is the tightest cross-section the saw has to work with along the log's whole length, so it sets the ceiling on how wide a board can come out anywhere in that log. Scale off the large end instead and every one of these numbers overstates what the log can actually yield.

The limits of a stick scale

None of these rules measure the log — they estimate it from two stick measurements and a fixed assumption about taper and kerf. A log with more sweep, more taper than the rule assumes, or hidden rot will cut less than its scale says; an unusually straight, clean log can sometimes cut more. That's true of every stick scale ever published, not just these three — it's the tradeoff for being fast enough to use on a landing or a scale ticket. These rules were built to standardize buying and selling logs quickly in the field, not to plan an actual cut. If you want the real recoverable volume of a specific log — not an estimate — scan it.

Frequently asked questions